1. Field of the Invention
The present invention relates to a molded surface fastener made of thermoplastic synthetic resin material having engaging elements each having a novel shape, which are integrally molded on a surface of a flat substrate independently of each other, the surface fastener having a particular function, and also relates to molding method and molding apparatus therefor. More specifically, it relates to a molded surface fastener which can be molded in various sizes from minute size to normal size, is suitable for various applications owing to its novel shape and function and can be produced continuously with a high efficiency by a single process by a simplified production apparatus, and a molding apparatus and molding method therefor.
2. Description of the Related Art
Conventional molded surface fasteners are manufactured in various methods. One typical manufacturing method is complete batch manufacturing method by injection molding. According to another typical manufacturing method, a die wheel having a plurality of engaging-element-molding cavities on a peripheral face thereof is driven and rotated in one direction and molten resin material is introduced continuously to the peripheral face of the die wheel so as to mold a flat substrate with engaging elements continuously and integrally. According to these methods, engaging elements of various shapes such as palm-like, hook-like or the like can be molded.
According to still another method, a plurality of substantially T-shaped engaging-element-molding extruding ports are provided in an extruding die and a flat substrate molding extruding ports are formed by communicating bottoms of the respective T-shaped extruding ports with each other. By extruding molten resin from the extruding ports at the same time, a plurality of ribs each having a substantially T-shaped cross section on a surface of the flat substrate are molded continuously and the molded molten resin material is hardened. Then, with the flat substrate remained, the aforementioned ribs are cut in a direction perpendicular to an extending direction of the ribs or at an appropriate inclination angle into a predetermined thickness successively, so that substantially T-shaped engaging elements are formed. By extending the flat substrate in a molding direction after the cutting, the cut individual engaging elements are separated with a desired pitch, thus a molded surface fastener is produced.
According to these molding methods, the shapes and dimensions of the engaging elements are limited if productivity thereof is engaged. On the other hand, if the shapes and dimensions of the engaging elements are provided with variety to some extent, it is difficult to mold them continuously or the quantity of production steps is increased, so that productivity decreases. In either case, these methods have both advantages and disadvantages.
Particularly, according to the above-mentioned method in which a drawing process is performed after the ribs of molten resin molding material on the surface of the flat substrate are cut from the extruding die and in which an engaging head portion can have a variety of sectional shapes to some extent, four steps, i.e. extrusion, rib cutting, heat drawing and cooling are required as disclosed in, for example, Japanese Patent Publication No. 53-22889. Of these steps, particularly the rib cutting requires a high processing accuracy, so that a quite large amount of labor and time are consumed for maintenance and control therefor.
The above-mentioned publication discloses a proposal that the aforementioned rib cutting process should be simplified and the heating extension process should be eliminated. According to this proposal, an extrusion-molded product having a plurality of ribs on the surface of the flat substrate is introduced onto a rotating drum and rotated substantially by a half turn in accordance with a rotation of the drum. During this rotation, two cutting blades, which are disposed in parallel to a rotation axis of the drum, of a cutting device are reciprocated in a direction of a chord with respect to the peripheral face of the drum so that the ribs are cut. At this time, a cutting angle when the extruded product is rotated on the peripheral face of the drum is utilized. By cutting twice with a difference of phase of about 80xc2x0 along the peripheral face of the drum, the ribs is cut into a V shape. Then, engaging elements whose front shape is substantially T shape and side view is substantially isosceles triangle are formed continuously.
However, in not only the aforementioned molded surface fastener produced by the cutting as mentioned above but also the molded surface fastener molded by the conventional molding cavities, a flat surface is necessarily formed on at least one of the side faces or front or rear faces of an engaging element, so that an edge portion is formed between the adjacent flat faces. This edge portion is likely to cut a loop which is a mating engaging element at the time of engagement and gives an uncomfortable feeling when touched.
In a molded surface fastener except the aforementioned extruded fastener, a configuration of a molding cavity needs to be complex if a shape of an engaging element is designed to be complex. However, such a complex molding cavity cannot be produced, so that necessarily only an engaging element of a simple shape can be obtained. On the other hand, in the molded surface fastener produced by extrusion, at least the front shape of each engaging element can be complex. However, because the molded ribs are separated into individual engaging elements by cutting the molded rib, its front and rear end faces of the engaging element are only a combination of the aforementioned flat surfaces. Therefore, a further complex configuration such as the one having curved faces is difficult to produce.
According to not only the manufacturing method of the surface fastener by extrusion and cutting but also the manufacturing method of the surface fastener by a die wheel or molding die, the flat substrate and engaging elements are entirely cooled at the same time. Therefore, the flat substrate and engaging elements of a completed surface fastener are the same in materiality. If they are cooled rapidly after molded, crystallization is not accelerated so that the entire structure becomes flexible. Consequently, the engaging strength and peeling strength may become insufficient. If they are cooled gradually, on the other hand, the crystallization is accelerated so that the entire hardness is increased. Consequently, the engaging strength and peeling strength increase and at the same time, the hardness of the flat substrate is also increased, so that the surface fastener becomes entirely stiff.
Further, in the engaging element of the aforementioned surface fastener produced by extrusion and cutting, a front or rear cross section of the engaging element perpendicular to the extruding direction is always the same. Particularly, it is impossible to mold an protruding end of the engaging element at a sharp angle. Thus, when the engaging element are a male one having equal dimensions, especially if a loop of a mating female engaging element is minute, the male engaging element cannot invade into the loop easily. As a result, the engagement rate drops, so that sufficient engaging strength and peeling strength cannot be secured.
The present invention has been achieved to solve the above described problems and an object of the invention is to provide a molded surface fastener which ensures an improved engagement rate, sufficient engaging strength and peeling strength although it has engaging elements each having a novel shape that did not exist in a conventional art and is entirely provided with high flexibility, and an effective manufacturing apparatus and method thereof.
The inventors of the present invention have already publicized a molded surface fastener which is a basis of the present invention as well as a molding apparatus and method thereof via Japanese Patent Laid-Open Publication No. 11-206422. The present invention has been obtained by further developing the invention that was disclosed in said publication. That is, in the aforementioned disclosed invention of said publication, the configuration of the molded surface fastener, for example, is not sufficiently stabilized. Therefore, the apparatus and method as well require further consideration in order to achieve the configuration stabilization of the product. Therefore, a number of considerations were taken even after the aforementioned proposal was submitted.
As a result, it was recognized that if viscosity of the molding resin is adjusted appropriately, the configuration of the product can be stabilized and that the configuration is a novel one that was not seen conventionally, which is a feature of the present invention. Further, it was also recognized that a physical property different from the conventional one can be gained, and that molding principle is not misunderstood. However, the viscosity of the molding resin differs depending on the molding material and molding condition. Therefore, the viscosity cannot be specified uniformly for all kinds of the molding materials or all kinds of molding conditions.
As a result of further accumulated considerations and experiments, the inventors of the present invention have achieved an invention on a molded surface fastener, a molding apparatus and a molding method for the molded surface fastener, which are described below. Consequently, products having the aforementioned physical property can be produced efficiently in a stabilized condition so that the aforementioned object can be achieved effectively.
According to a first aspect of the present invention, there is provided a molded surface fastener comprising a flat substrate and a plurality of first engaging elements molded of the same material integrally with each other, wherein the engaging element is composed of a stem portion standing from a surface of the flat substrate and an engaging head portion protruded from a tip of the stem portion at least in one side direction perpendicular to a molding direction thereof; a thickness of the first engaging element in a direction perpendicular to the protruding direction of the engaging head portion increases gradually from a top portion of the engaging head portion to a base end of the stem portion; and lateral widths between front and rear end faces of the engaging head portion of the first engaging element in the molding direction are different from each other.
The molded surface fastener having such a specific configuration of the present invention can be molded in a stabilized condition according to a molding apparatus and method that will be described later. Because in the above molded surface fastener, the thickness of the first engaging element increases gradually from the top portion of the engaging head portion to a base end of the stem portion, the engaging element is not bent easily by a force (shearing force) parallel to the surface of the flat substrate or a pressing force acted obliquely from above the substrate. When a loop which is a mating female engaging element is pulled obliquely upward in a condition that it engages the stem portion, the loop is necessarily introduced to a border area between the stem portion and engaging head portion, so that the engaging head portion does not become loose in the loop, thereby the engagement not being released easily. Further, because the width of each engaging element in a back and forth direction increases gradually from the top portion to front ends thereof, the engaging element is more likely to be inserted into the mating loop when it is pressed for engagement.
Further, protruding lengths of the front and rear end faces of the engaging head portion of the first engaging element which is a feature structure of the present invention are different. That is, when the engaging head portion is seen from top, it assumes a substantially trapezoidal shape. An end portion on the front end face side extending longer is a sharp edge, so that it is more likely to be inserted into a loop which is a mating female engaging element. As a result, the engagement rate is improved and total engaging strength is increased, owing to the above described structure as well.
Because an opening shape of the first engaging-element-molding openings in the molding apparatus of the present invention can be formed arbitrarily, a shape of the first engaging element as viewed from front can be formed in diversified dimensions and shapes such as substantially T shape, substantially Y shape, palm tree shape, a single hook shape, a mushroom shape or their combination or such that its external contour as viewed from front is curved. Further, a height or a length of the engaging element can be changed freely.
Further, a plurality of second engaging elements are molded on a back surface of the flat substrate. Therefore, because the molded surface fastener of the present invention has the first and second engaging elements on the front and rear faces thereof, the engaging faces of the female surface fasteners can be engaged with each other via the molded surface fastener of the present invention. Each of the second engaging elements to be molded on the rear face of the flat substrate can be formed in diversified shapes as conventional ones such as the hook shape, palm tree shape, T shape, Y shape, and mushroom shape.
Furthermore, lateral widths of front and back end faces of the stem portion of the first engaging element in the molding direction are different from each other. Because the stem portion also provides a substantially trapezoidal shape as well as the above described shape of the first engaging element, the shape of the engaging element during use is stabilized so that its initial engaging/disengaging function is maintained for a long time even if it is used repeatedly.
Still further, there is provided a molded surface fastener, wherein hardness of the flat substrate is set lower than hardness of the engaging head portion. Conventionally, in this kind of the molded surf ace fastener, through hardening by cooling after a product is molded is rapid cooling or gradual cooling, the flat substrate and engaging elements are hardened by cooling under the same condition. Therefore, an entire product has a substantially equal hardness. As a result, if flexibility is regarded as important, the engaging element itself becomes flexible, but the engaging strength decreases. If the engaging strength is regarded as important, the entire product becomes stiff. Consequently, applications of the product are limited. However, according to the present invention, because the hardness of the substrate is lower than that of the engaging element but the entire surface fastener is sufficiently flexible but the engaging element still maintains a desired hardness. Thus, owing to the above described specific configuration as well, the engaging element is not bent easily by a pressing force of a mating female surface fastener member. Consequently, the engagement rate with the loops which are the mating engaging elements is improved largely, so that its application field is expanded largely.
Still further, a shorter-width rear end face of the engaging head portion of the first engaging element in the molding direction, assuming a substantially trapezoidal shape as viewed in plan, is curved in the width directions and bulges backward. With such a structure, the engaging loops, which are the mating female engaging elements, becomes easy to move forward along the curved rear end face when disengaged. Thus, different from the conventional rectangular engaging head portion, a smooth disengaging operation is enabled without deforming the engaging head portions excessively. On the contrary, after the protruding end of each engaging head portion is inserted into the loop which is the mating female engaging element, the loop is introduced smoothly up to the border between the engaging head portion and stem portion along the curved face of the engaging head portion. Thus, there exists no edge portion between flat surfaces unlike conventional ones, and therefore a secure engagement can be achieved.
Still further, rear end faces of the stem portion and engaging head portion of the first engaging element in the molding direction are composed of curved faces continuous in a vertical direction thereof. Conventionally, an engaging element in which an end face of an engaging head portion and an end face of a stem portion opposite to the extending direction of the engaging head portion are composed of curved faces has been well known. In case of the molded surface fastener, usually, right and left end faces perpendicular to the extending direction of the engaging head portion are composed of parallel flat faces. However, in the first engaging element of the present invention, of front and rear end faces perpendicular to the extending direction of the engaging head portion, at least the rear end face of the engaging head portion and stem portion, which is an end face opposite to the molding direction, is curved vertically. The right and left end faces corresponding to the aforementioned flat faces at the right and left end faces of the conventional engaging element can be molded in an arbitrary curved face by setting second openings in the extrusion nozzle of the molding apparatus according to the present invention in an arbitrary shape.
Because most the contour of the engaging element can be composed of curved faces, not only tactile feeling is excellent but also when the surface fastener is engaged, a loop which is a mating female engaging element can be introduced into the engaging head portion easily. Further, when the surface fastener is disengaged, it can be released without applying an excessive force upon the loop. That is, the surface fastener can be engaged or disengaged smoothly.
Still further, the flat substrate has a concave groove which is located between first adjacent engaging elements along the protruding direction of the engaging head portion and continuous perpendicular to the protruding direction. By forming the concave groove in the surface of the substrate, an actual thickness of the flat substrate is reduced with respect to an apparent thickness thereof so as to increase flexibility and at the same time, prevent an occurrence of cracks in the substrate between the engaging elements adjacent in their back and forth direction. Further, side walls of the concave groove functions as a guide face for introducing a mating loop to the base end of the engaging element, thereby improving the engagement rate with the loop.
Still further, orientations of resin material on surface portions of the front/rear end faces and right/left side faces of the stem portion and engaging head portion respectively, and a top portion of the engaging head portion of each first engaging element are directed in the molding direction.
In the surface fastener molded according to a molding principle which is a feature of the present invention, a large tensile strength parallel to the molding direction of the flat substrate exists. This tensile strength can be expected in the conventional method for molding the engaging elements with the engaging-element-molding cavities. However, a tensile strength in a vertical direction along the front and rear end faces in the molding direction of the engaging element is increased largely according to the present invention, which cannot be expected in the aforementioned molding method for molding the engaging elements by cutting and extending after ribs are extruded. Therefore, a rupture strength of the engaging element is increased. By molding the front and rear end faces in the molding direction, the right and left end faces and the top portion of the engaging head portion of the engaging element by extrusion and vibration of the vertically vibrating member when the engaging elements are molded according to the present invention, resin material on all the surface layer portion of the engaging element is oriented in the molding direction, so that the tensile strength in the molding direction is increased.
A passing speed of the molten resin at this time is constant. When a vibration speed of the extrusion nozzle is changed, an increased amount of the resin passing through the openings within a unit time becomes a molded amount in a rotating direction of a die wheel, so that the molded engaging element becomes longer in the rotating direction of the die wheel. According to the present invention, it is possible to arbitrarily determine a molding length of the first engaging element by controlling the vibration speed to be constant or varied. Specifically, it is possible to make the same lengths of the first engaging elements by setting the vibration speed to be constant. Alternatively, it is possible to vary the lengths of the first engaging elements by changing the vibration speed during the molding.
The molded surface fastener having such a configuration is molded effectively by means of a molding apparatus which will be described below.
According to a second aspect of the present invention, there is provided a molding apparatus for molded surface fastener for molding a flat substrate and a plurality of engaging elements integrally and continuously using the same molding material, comprising: a cooling/transportation means adapted to be driven and rotated in one direction for molding and transporting at least part of the flat substrate between an extruding die and the cooling/transportation means; an extrusion nozzle disposed at an end side of transportation by the cooling/transportation means of the extruding die, opposing a rotating transportation face of the cooling/transportation means and having a resin extrusion path which is open in a transportation direction; at least an vertically vibrating member disposed in front of the resin extrusion path for opening/closing vertically at least part of the resin extrusion path; and at least a vibrating means for vibrating vertically the vertically vibrating member, wherein the resin extrusion path has at least plural first engaging-element-molding openings spaced in the width direction.
The vertically vibrating member is preferably composed of a plate-like member.
A basic molding principle of the surface fastener of the present invention is the same as the molding principle of the surface fastener proposed by the inventors of the present invention in Japanese Patent Laid-Open No. 11-206422. However, the molding apparatus of the present invention has features in the following points. First, in order to mold the surface fastener continuously, molten resin is extruded from the extruding die directly to a cooling/transportation face of the cooling/transportation means driven an rotated in one direction. Second, the molten resin extruded to the cooling/transportation face and carried on the cooling/transportation face continuously is introduced through the resin path and molded to be the first engaging elements on the flat substrate face successively by means of the vertically vibrating member on a front face of the first engaging-element-molding openings.
The molten resin extruded from the extruding die to the cooling/transportation face is cooled directly by the transportation face so that hardening thereof is started. Then, while the molten resin passes through the resin flow path, it is molded to have an engaging element cross section defined by the flow path and at the same time the cooling is accelerated up to inside of its structure. As a result, the entire hardness is intensified more than the molten state just after it is extruded from the extruding die and then, the resin hardened is molded to be a shape of the engaging element by vibration of the vertically vibrating member. Because the engaging elements are molded by the vibration of the vertically vibrating member in half molten state in which a higher hardness is secured than that when the molten resin is extruded from the extruding die, contraction which may occur when molded can be suppressed and dragging of resin by the vertically vibrating member can be also restrained, so that a much stabilized desired shape can be obtained.
Because the molded resin is cooled most rapidly in the flat substrate and the cooling speed is retarded as it goes toward a vertex of the engaging head portion of the first engaging element, crystallization of the engaging element is progressed more than the crystallization of the flat substrate when a final product is produced. As a result, hardness of the flat substrate is lower than that of the first engaging elements and therefore, although flexibility of the entire surface fastener is secured, a desired hardness and a sufficient engaging strength are secured in engaging element.
Further, the cooling/transportation means is composed of a cooling drum adapted to be driven and rotated in one direction. Instead of a conventional expensive die wheel having engaging-element-molding cavities on its peripheral face, the cooling drum having a smooth surface can be employed. Further, the molding apparatus can be produced only by adding the extrusion nozzle and the up/down vibrating means to a conventional extrusion die. Thus, no consideration upon increase of production cost and equipment space is needed.
On the other hand, according to the present invention, a plurality of second engaging-element-molding cavities may be formed on a peripheral face of the cooling drum. Instead of mainly forming the engaging-element -molding cavities in the surface of the drum, it is permissible to use an existing die wheel already having the engaging-element-molding cavities in its peripheral face. Therefore, the first engaging elements can be molded in the surface of the flat substrate by vibration of the vertically vibrating member and at the same time, the second engaging elements are molded integrally in the rear surface of the same substrate. As a result, the molded surface fastener having the first and second engaging elements on the front and rear surfaces thereof can be molded continuously.
As for the aforementioned cooling means, it is permissible to circulate refrigerant within the rotation drum or immerse half of the rotation drum in a cooling water bath. The cooling/transportation means does not always have to be a drum body, but the cooling endless belt which is to be rotated by driving in one direction may be used. In this case, the endless belt may be made of a steel belt and both ends which are guided by driving/cooling rolls. And a flat supporting member for supporting the belt transportation face rotated by driving between the rolls from inside may be disposed. Of course, it is preferable that the aforementioned supporting member itself be structured as a cooling body.
Furthermore, the vertically vibrating member is comprised of comb-teeth-like first and second vertically vibrating members having opening portions formed such that they do not overlap each other laterally, and the first and second vertically vibrating members are disposed against a front face of the resin extrusion path of the extrusion nozzle and adapted to be lifted up and down alternately by corresponding vibrating means. With such a structure, in a molded surface fastener, a plurality of the engaging elements stands integrally from the surface of the flat substrate in staggered arrangement. Therefore, the engagement rate with the mating loop is distributed equally to an entire surface of the flat substrate.
Still further, a gap between the extrusion nozzle and the cooling/transportation means is set substantially the same as a minimum thickness of the substrate. When the vertically vibrating member opens or closed the engaging-element-molding openings in a vertical direction, a flat substrate having the same thickness as the aforementioned gap is formed. When the vertically vibrating member descends in order to close the engaging-element-molding openings with a desired substrate left, the base ends of the stem portions are left continuously in the molding direction. As a result, a concave groove continuous in the molding direction is formed in the flat substrate.
According to a third aspect of the present invention, there is provided a molding method for molded surface fastener for molding a flat substrate and a plurality of first engaging elements integrally and continuously using the same molding material, comprising steps of: driving and rotating a cooling/transportation means for cooling and transporting a molded surface fastener in one direction at the same time when it is molded; extruding molten resin material continuously onto a cooling/transportation face through a resin extrusion path which extends in a width direction of an extrusion nozzle and which is open to the cooling/transportation face of the cooling/transportation means and opens in a transportation direction thereof; and opening/closing the plurality of first engaging-element-molding openings spaced in the width direction of the resin extrusion path by means of at least an vertically vibrating member comprised of a plate-like member disposed on a front face of the extrusion nozzle in a resin transportation direction.
The above described molding method enables to manufacture the molded surface fastener having the aforementioned configuration continuously in a single production step so that its production unit cost becomes reasonable. On the other hand, in manufacturing a molded surface fastener having the similar configuration according to the conventional extrusion-molding in which a plurality of the ribs each having a T-shaped cross section are formed to stand from the surface of the substrate for example, the rib is cut with a predetermined thickness in a longitudinal direction thereof and then, the cut rib is drawn in a longitudinal direction thereof. Thus, this method is not efficient because plural manufacturing steps are required. Further, front and rear faces of the engaging element of a produced molded surface fastener in the longitudinal direction are flat surfaces parallel to each other because they are composed of cut surfaces as mentioned above. If this is compared with the configuration of the engaging element of the present invention, the engaging element is more likely to fall down in its back and forth direction and its production unit cost is necessarily higher than that of the present invention.
According to the molding method of the present invention, when molten resin is extruded from the extruding die of an extruder directly to the cooling/transportation face of the cooling/transportation means, the extruded molten resin is carried by the cooling/transportation face through the molten resin flow path in the extrusion nozzle. At this time, a contact surface of the molten resin extruded to the cooling/transportation face with the cooling/transportation face is cooled positively so that hardening is started. Then, that cooling is transmitted to the molten resin extruded from the molten resin flow path so that the molded portion of the flat substrate and the molded portions of the first engaging s elements are cooled gradually. The molded portion of the first engaging elements are slightly hardened and becomes into a half molten state at the first engaging-element-molding openings. Then, front and rear faces of the first engaging elements are molded at the openings by an up/down motion of the up/down vibration member.
At this time, a lower limit position of the vertically vibrating member is, for example, such a position that leaves a thickness of the substrate. Specifically, when the molten resin is always extruded from a gap between the extrusion nozzle and the cooling/transportation face in form of a flat sheet, and the vertically vibrating member ascends and descends to the lower limit position so as to mold the first engaging elements successively on a top surface of the flat substrate continuously.
That is, after the vertically vibrating member arrives at the lower limit position, it starts to ascend, so that the engaging-element-molding openings open gradually upward from the lower limit. At this time, the flat substrate whose hardening is progressed is carried continuously by the cooling/transportation face and at the same time, the stem portions and engaging head portions of the first engaging elements are molded along the shape of the openings by extruding successively from a lower portion thereof depending on a degree of their openings, in a state in which the molded portion of the first engaging element is slightly hardened. Finally, the vertically vibrating member reaches the top limit of the openings to mold front end faces of the stem portions and engaging head portions, thus completing molding of front faces of tops of the engaging head portions.
When the lower end of the vertically vibrating member reaches the top end of the openings, almost front half portions of the engaging elements in the extruding direction are molded and then, the vertically vibrating member starts to descend. It closes the engaging-element-molding openings gradually from the top end so as to mold rear half portions of the engaging elements from a top portion thereof to base ends of the stem portions along a reverse step to the molding of the front half portions. Because the molten resin molded by the vertically vibrating member is slightly hardened and has a uniform hardness at this time, the molded shape is stabilized.
Further, due to the cooling mechanism provided by the cooling/transportation means, a surface fastener having a physical property particular to the present invention, which could not be expected in the conventional surface fastener, can be molded. That is, due to a difference of the cooling mechanism between the flat substrate and the engaging elements at the time of molding, hardening of the flat substrate is accelerated based on the positive cooling and as a result, the hardening is completed before crystallization is completely achieved. On the contrary, the engaging elements are cooled by transmission. Thus, the hardening of the engaging elements is delayed, so that crystallization is accelerated and the hardness thereof becomes higher than the substrate. Therefore, although the molded surface fastener is provided with a sufficient flexibility, the engaging strength of the engaging elements is increased. Further, due to the high hardness, the engaging elements are unlikely to be deformed, so that the engagement rate and peeling strength are also increased.
According to the present invention, the half molten thermoplastic resin material extruded from the first engaging-element-molding openings each having a desired cross section of the first engaging element is molded continuously by moving up and down the vertically vibrating member. Thus, resin material of the surface portions of the stem portion, engaging head portion, and top portion of the engaging head portion are oriented in the molding direction. As a result, tensile strength of all the surface portion of the flat substrate and engaging elements in the molding direction is improved so that a rupture strength of the engaging element is improved largely.
On the other hand, a front view shape of the molded engaging element substantially coincides with the shape of each engaging-element-molding opening. Although the front end face shape and rear end face shape as viewed in the molding direction are analogous, the lateral width of the former is slightly larger than that of the latter. This is considered to be generated due to a difference of behavior of extruded molten resin when the vertically vibrating member, which moves up/down on the front faces of the engaging-element-molding openings, opens or closes that openings. That is, when the engaging-element-molding openings are closed, resin pressure is intensified by an extruding pressure because it is enclosed in the resin extruding flow path. Then, when the vertically vibrating member moves upward, the opening is opened suddenly so that the aforementioned resin pressure is released for an instance and more resin than in the normal state is extruded. However, when the vertically vibrating member descends so as to close the openings, extrusion of the molten resin is interrupted instantly. Thus, the extruding amount of the resin may drop below a set value. Consequently, there is generated a difference of the lateral width between the front and rear end faces in the molding direction of the engaging head portion of the first engaging element, which constitutes the feature portion as described above.
On the other hand, as for a side view shape of the first engaging element, it is expanded like a skirt in the back and forth direction of the molding direction with a curve from its top end to its bottom end. Further, by changing a lift-up/down speed of the vertically vibrating member in various ways, the curve expanding like a skirt in the back and forth direction can be changed in diversified shapes. The side view shape is determined by the lift-up/down speed of the vertically vibrating member.
As a result, a surface fastener having a configuration and function which could not be expected in this kind of the conventional surface fastener extrusion molding can be obtained, and efficient molding by a single step which could not be expected in the conventional molding method can be carried out.
Further, a plurality of second engaging elements may be molded integrally on a surface of the flat substrate on an opposite side to the surface on which the first engaging elements are molded at the same time. This molding is achieved by forming the second engaging-element-molding cavities in the transportation face of the cooling/transportation means. In this case, a conventional die wheel having a plurality of the engaging-element-molding cavities on its peripheral face may be used. A surface fastener molded according to this method becomes double-sided molded surface fastener. Depending on the configuration of the engaging element, not only self bonding performance is possessed but also products having loop faces can be joined together via this surface fastener.